The Stirling Cycle is characterized by its capability of running on not only a combustion heat source but also on other heat sources with various temperature differences, such as waste heat and solar heat. Obtaining maximum output from heat sources with various temperature ranges requires an optimization of balance between the volumetric change of working gas and the gas flow passing through the regenerator in accordance with the temperature difference.
Specifically, use of a heat source with a smaller temperature difference, such as waste heat and solar heat, needs a larger ratio of gas flow passing through the regenerator to the volumetric change. The reason is as follows. The source of output of the Stirling Cycle in this case is the rise in gas pressure at the time when the gas passes through the regenerator. A smaller temperature difference renders a smaller rise in pressure relative to the gas flow passing therethrough. Accordingly, obtaining a maximum output from a heat source with a smaller temperature difference needs an increase in gas flow passing through the regenerator relative to the volumetric change in comparison to the gas flow in a case of using a heat source with a larger temperature difference.
Incidentally, there exist roughly three types of conventional configuration substantiating the Stirling Cycle: an α-configuration, a β-configuration and a γ-configuration. The α-configuration has a power piston in the high-temperature space and another power piston in the low-temperature space, so that the configuration of this kind is also called a two-piston configuration. With this configuration, each of the two pistons in each space sweeps the gas out completely. The extremely small clearance volume thus accomplished is a characteristic of this configuration.
The above-mentioned ratio can be changed by changing the phase difference between the displacement of one of the two piston and that of the other. In a case of a heat source with a smaller temperature difference, the optimization is possible by increasing the phase difference in accordance with the temperature difference. For example, though a 90° phase difference renders an optimum result for a large temperature difference of 500° C. or larger, the phase difference is increased to approximately 150° for a smaller temperature difference around 100° C. (see Patent Document: Japanese Patent No. 3134115).